Automatic Primary Key Generation

With Workshop for WebLogic you can specify in your bean code that a primary key should automatically be generated when creating a new CMP entity bean. This eliminates the need for you to provide primary key
values. You can auto-generate primary keys in various vendor-specific ways
— using Oracle, SQLServer, or SQLServer2000 — or you can use a vendor-neutral
named sequence table. In all cases auto-generated primary keys are of type Integer or Long.

Primary Key Generation Using Oracle's
Sequence

Oracle provides the sequence utility to automatically generate unique primary
keys. To use this utility to auto-generate primary keys for a CMP entity bean,
you must create a sequence table and use the @AutomaticKeyGeneration
annotation to point to this table.

In your Oracle database, you must create a sequence table that will create
the primary keys, as shown in the following example:

create sequence myOracleSequence
start with 1
nomaxvalue;

This creates a sequences of primary key values, starting with 1, followed by 2,
3, and so forth. The sequence table in the example uses the default increment
1, but you can change this by specifying the increment
keyword, such as increment by 3. When you
do the latter, you must specify the exact same value in the cacheSize
attribute of the @AutomaticKeyGeneration annotation:

If you have specified automatic table creation in the CMP bean's project
settings, the sequence table will be created automatically when the entity
bean is deployed. For more information, see @JarSettings
Annotation. For more information on the definition of a CMP entity bean,
see below.

Primary Key Generation Using SQL Server's
IDENTITY

In SQL Server you can use the IDENTITY keyword to indicate that
a primary-key needs to be auto-generated. The following example shows a
common scenario where the first primary key value is 1, and the increment
is 1:

If you have specified automatic table creation in the CMP bean's project
settings, the sequence table will be created automatically when the entity
bean is deployed. For more information, see @JarSettings
Annotation. For more information on the definition of a CMP entity bean,
see below.

Primary Key Generation Using a Named Sequence Table

A named sequence table is similar to the Oracle sequence functionality
in that a dedicated table is used to generate primary keys. However, the
named sequence table approach is vendor-neutral. To auto-generate primary
keys this way, create a named sequence table using the two SQL statements
shown in the example:

If you have specified automatic table creation in the CMP bean's project
settings, the sequence table will be created automatically when the entity
bean is deployed. For more information, see @JarSettings
Annotation. For more information on the definition of a CMP entity bean,
see the next section.

Note. When you specify a cacheSize value for
a named sequence table, a series of unique values are reserved for entity
bean creation. When a new cache is necessary, a second series of unique
values is reserved, under the assumption that the first series of unique
values was entirely used. This guarantees that primary key values are always
unique, although it leaves open the possibility that primary key values
are not necessarily sequential. For instance, when the first series of
values is 10...20, the second series of values is 21-30, even if not all
values in the first series were actually used to create entity beans.

Defining the CMP Entity
Bean

When defining a CMP entity bean that uses one of the primary key generators,
you use the the @AutomaticKeyGeneration annotation to point to the name of the primary key generator table to obtain primary
keys.
Also, you must define a primary key field of type Integer
or Long to set and get the auto-generated
primary key. However, the ejbCreate method
does not take a primary key value as an argument. Instead the EJB container
adds the correct primary key to the entity bean record.

The following example shows what the entity bean might look like.
Notice that the bean uses the named sequence option described above, and
that ejbCreate method
does not take a primary key: